Flexible electronic devices and related methods

ABSTRACT

A packaged electronic device includes a flexible circuit structure and a die. The flexible circuit structure includes a first structural layer and electrical conductors. The die is bonded to the flexible circuit structure by a flexible attachment layer. The die includes interconnects in electrical contact with die circuitry and extending through the die, through the flexible attachment layer, and into electrical contact with respective electrical conductors at first ends. A flexible second structural layer is disposed on the die and exposed portions of the electrical conductors, wherein the die and the electrical conductors are encapsulated by the first structural layer and the second structural layer. The first structural layer and/or the second structural layer include a plurality of openings defining respective exposed areas on the electrical conductors at second ends.

RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/US2010/038366, filed Jun. 11, 2010, titled “FLEXIBLE ELECTRONICDEVICE AND RELATED METHODS”, the content of which is incorporated byreference herein in its entirety.

TECHNICAL FIELD

This invention relates generally to electronic devices and the packagingthereof, including but not limited to hermetic and/or biocompatiblepackaging or sealing that renders such electronic devicesenvironmentally isolated and/or implantable in vivo or in vitro. Moreparticularly, the invention relates to electronic devices that includeflexible circuit structures integrally bonded to and embedded with diestructures, and assemblies or systems that include or cooperate withsuch electronic devices.

BACKGROUND

An ongoing need exists for advances in electronic deviceminiaturization, packaging of integrated circuits and associatedmicrofabrication technologies to enable new and improved implementationsof electronic devices. Up to the present time, flip-chip technology asapplied to bare dies has been considered to be the assembly processachieving the highest packing density, smallest footprint and lowestprofile. For a detailed discussion of trends and challenges instate-of-the-art chip packaging (chip scale packaging, CSP andflip-chip), see Fjelstad et al., Chip scale packaging for modernelectronics, Electrochemical Publications Ltd. (2002); Quinones et al.,Flip-chip and chip scale packaging technologies: A historicalperspective and future challenge, SEMICON China 2000 TechnicalSymposium: A1-A9 (2000). Briefly, in the flip-chip process the die isassembled face down onto the substrate (rigid board or flexible) with anarray of solder bumps making electrical connection to the substrate.Reliability of the interconnects in flip-chip has been a great concernin the industry. This is particularly true for bonding to organicsubstrates because of the difference in thermal expansion coefficientsbetween the chip and the substrate. Usually epoxies are used asunderfill materials to make structures mechanically stronger and toimprove reliability.

The need for further advances extends to environmentally isolated and/orbiocompatible devices. Examples of biocompatible devices includeimplantable neural prostheses designed to interface with the nervoussystem to restore lost functions such as movement, hearing or vision.Other examples of neurostimulation devices include, without limitation,devices envisioned for spinal cord stimulation, deep brain and vagusnerve stimulation, sacral nerve stimulation, and gastric electricalstimulation. The requirements for such advanced implants are verydifferent from implant devices found in the market today. The best knownand commercially most successful implant is the cardiac pacemakerdeveloped more than 30 years ago. Like the pacemaker, many of theFDA-approved implant devices use rigid packaging like titanium orceramic casings for hermetic sealing and are equipped with mostly singleor low-density microelectrodes for sensing and delivery of electricalstimulation. The electrodes and insulation are “oversized” and thedevices are engineered for minimal failure incidents. Therefore, suchdevices are very bulky, limited in their functionality and require veryinvasive implantation procedures.

To enable new neurotechnology devices to interface effectively with thenerve system and to open up new applications, miniaturized and moreflexible device structures with improved spatial and temporalsensitivity and packaging are needed. For many important applicationssuch as the retinal implant where the shape of the implant structureneeds to adapt to the curved shape of the inner eye, the substrateshould be flexible to conform to the natural soft-tissue structure. Thatis, many types of implantable devices should ideally be biocompatiblenot only in the sense of chemical and biological inertness, but also inthe sense of “mechanical” or “structural” biocompatibility, i.e.,sufficient physical conformability and flexibility so as not to interactwith surrounding tissue in an unwanted manner.

In recent years, researchers have focused on the use of flexiblesubstrates like polyimides (or more recently liquid crystal polymers(LCP), or benzocyclobutene (BCB)) with hybrid assemblies of electronicchips, conduction layers and microelectrode arrays for stimulating andrecording, all integrated on the flex substrate. A small footprint, highfunctionality, high reliability and biocompatibility are desirableattributes for active medical implants. The smaller the device, the lessinvasive is the procedure of implantation and one can expect bettercompatibility with surrounding tissue. At the same time, as noted abovedevices need to be packaged to have a biocompatible tissue interface andto withstand biodegradation in the body. The term biocompatibility inthis context refers to mechanical biocompatibility as well asimmunological biocompatibility.

The development of flexible polymer carriers for mounting andinterconnecting chips and miniaturized components offer the possibilityto develop micro-electronic and micro-optical systems that are in directcontact with delicate soft tissues and biological structures. Instead ofstandard housed IC components, bare or “naked” silicon chips and diesare used for hybrid integration to minimize component dimensions.

Unresolved critical issues in all implantable biomedicalapplications—and particularly for implanted neural prostheses and otherdevices envisioned to include flexible polymeric substrates—includepackaging, integration and electrical connection of silicon dies orsurface mounted electronics with the substrate and electrode arrays.Major challenges include bonding of chips or dies to flexible substratesand packaging of the device including electrical interconnects,connection pads and cables/leads. Protecting the implant from thecorrosive effects of the biological fluids has been a particularchallenge. Insulating biomaterials intended for implants need to protectdevices from the hostile body environment for the lifetime of an implantrecipient, sometimes for decades. Not only does the packaging need towithstand biodegradation in the body, but also the materials need to bebiocompatible to prevent adverse reactions from the surrounding tissue.To date, the goal of a functional neural implant device that can survivefor years in vivo or in vitro has not been achieved.

Several companies use flip-chip processes to produce miniaturizedturnkey electronic assemblies for medical implants, micro/miniaturewireless devices, and a host of other applications. In addition tosolder bumps, flip-chip technology has also employed gold wire studbumps. Additionally, Parylene coatings have been employed forpassivation to assemble a prototype implantable retina prosthesis withsecondary receiving power and data coils. Researchers at the Universityof Utah are developing flip-chip assembly techniques to surface-mountchips directly on the back of a Si probe. See Solzbacher F., Chronicmicrolectrode arrays, Contract NINDS-NIH N01-NS-4-2362 (2004-2008). As amodification of traditional flip-chip processing, a group at theFraunhofer Institute for Biomedical Engineering, St. Ingbert, Germanyhas developed a flexible interconnection technology to interconnectchips and surface-mount passive devices (SMD) with ultra-thin highlyflexible polyimide (PI) substrates for a retinal implant using goldballs instead of solder bumps to connect the IC and substrate. SeeStieglitz et al., Micromachined, polyimide-based devices for flexibleneural interfaces, Biomed. Microdevices. 2(4): 283-294 (2000); Meyer etal., High density interconnects and flexible hybrid assemblies foractive biomedical implants, IEEE Trans. Adv. Pack. 24: 366-374 (2001).This new assembly process is known as MicroFlex Interconnection (MFI).First, the PI substrate with metal traces and connection pads with acentral via is microfabricated. The vias are aligned with the bond padsof the IC and a gold ball is bonded through the vias in the PI onto themetal pads of the chip utilizing a common thermosonic ball-bumpingprocess. The gold ball acts as a stud or metal “rivet” to electricallyconnect and mechanically fix the chip or SMD to the substrate. This is asimilar bonding scheme to flip-chip with gold studs replacing solderbumps. Because bonding occurs only at the through-via sites in the PIcable, an epoxy material is filled between the ribbon cable and the ICor SMD to improve stability of the connection. See Stieglitz et al.,Micromachined, polyimide-based devices for flexible neural interfaces,Biomed. Microdevices. 2(4): 283-294 (2000).

Known technologies such as discussed above have not adequately addressedthe above-mentioned problems. For instance, even with the use ofunderfill material, solder bumps, metal balls, rivets, and otherconventional interconnects still represent potentially weak connectionpoints, both structurally and electrically, between the chip or die andunderlying substrate. These types of interconnects as well as theunderfill material may still be prone to degradation in anenvironmentally or biologically hostile environment. Accordingly,mechanical stability, operational or functional reliability,biocompatibility, service life, etc. are still compromised inconventional packaged electronic devices. Moreover, sufficientminiaturization as needed for advanced devices such aselectrostimulation devices has not been attained. As an example in thecase of an intraocular implant such as an artificial retina, it isestimated that up to 1000 electrical neurostimulation sites are neededto restore useful vision in blind people. See Margalit et al., Retinalprosthesis for the blind, Survey Ophth. 47: 334-356 (2002). Currently,state-of-the-art retina chips have been designed and fabricated in thestandard CMOS process with 1.5-μm feature size through the MOSIS foundry(Marina Del Rey, Calif.) to address up to 64 sites on a 4.6 mm×4.6 mmchip at the University of Michigan. See Ghovanloo et al., A modular32-site wireless neural stimulation microsystem, IEEE J. Sol. State Cir.39:1-10 (2004). Other groups in the USA and in Europe have built chipswith similar capabilities and size. See Liu et al., A neuro-stimuluschip with telemetry unit for retinal prosthetic device, IEEE J. Sol.State Cir. 35: 1487-1497 (2000). It is not clear whether currenttechnology is sufficient to enable engineers to design and build thecircuitry to stimulate 1000 sites and package the circuitry into asingle chip with this footprint because of limitations in the I/O andconnections to substrate and the required voltage to stimulate neurons.Most likely, through the use of current technology, several chips wouldneed to be mounted on the flex substrate to attain the requiredperformance and functionality.

Therefore, in view of the foregoing, despite some advances inmicrofabrication technologies pertaining to packaged electronic devices,it is well-recognized by persons skilled in the art that an ongoing needexists for providing improved packaged electronic devices and relatedmethods, apparatus and systems.

SUMMARY

To address the foregoing problems, in whole or in part, and/or otherproblems that may have been observed by persons skilled in the art, thepresent disclosure provides methods, processes, systems, apparatus,instruments, and/or devices, as described by way of example inimplementations set forth below.

According to one implementation, a packaged electronic device includes aflexible circuit structure and a die. The flexible circuit structureincludes a first structural layer and a plurality of electricalconductors disposed on the first structural layer. The plurality ofelectrical conductors includes a plurality of respective first ends anda plurality of respective second ends. The die includes a first surface,an opposing second surface, and die circuitry formed on the firstsurface. The die is bonded to the flexible circuit structure by aflexible attachment layer interposed between the second surface and thefirst structural layer. The die further includes a plurality ofthrough-wafer interconnects in electrical contact with the die circuitryand extending through the die, through the flexible attachment layer,and into electrical contact with the respective electrical conductors atthe first ends. A flexible second structural layer is disposed on thedie and exposed portions of the electrical conductors, wherein the dieand the electrical conductors are encapsulated by the first structurallayer and the second structural layer. The first structural layer and/orthe second structural layer include a plurality of openings definingrespective exposed areas on the electrical conductors at the secondends.

According to another implementation, a method for fabricating a packagedelectronic device is provided. A plurality of electrical conductors isformed on a first structural layer. An attachment layer is deposited onthe electrical conductors and the first structural layer. A dieincluding die circuitry is placed on the attachment layer. A pluralityof interconnects is formed. The interconnects extend from the diecircuitry, through the die, through the attachment layer, and intocontact with respective electrical conductors. A second structural layeris deposited on the die and exposed portions of the electricalconductors, wherein the first structural layer and the second structurallayer encapsulate the die, the die circuitry and the electricalconductors. A plurality of openings is formed through first structurallayer and/or the second structural layer to expose respective areas ofthe electrical conductors.

Other devices, apparatus, systems, methods, features and advantages ofthe invention will be or will become apparent to one with skill in theart upon examination of the following figures and detailed description.It is intended that all such additional systems, methods, features andadvantages be included within this description, be within the scope ofthe invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood by referring to the followingfigures. The components in the figures are not necessarily to scale,emphasis instead being placed upon illustrating the principles of theinvention. In the figures, like reference numerals designatecorresponding parts throughout the different views.

FIG. 1A is a cross-sectional elevation view of an example of a packagedelectronic device operatively communicating with another electronicdevice, according to certain implementations of the present disclosure.

FIG. 1B is a plan view of the packaged electronic device illustrated inFIG. 1, with the other electronic device and certain structural featuresremoved.

FIGS. 2A-2J are cross-sectional elevation views illustrating an exampleof a method for fabricating a packaged electronic device such as thedevice illustrated in FIGS. 1A and 1B.

FIG. 3 is a plan view of an example of a substrate in which a pluralityof packaged electronic devices is being fabricated.

FIG. 4 is a cross-sectional elevation view of another example of apackaged electronic device in which a plurality of die is incorporatedin a planar arrangement along the length of the device.

FIG. 5 is a cross-sectional elevation view of another example of apackaged electronic device in which a plurality of die is incorporatedin a stacked arrangement along the height of the device.

FIG. 6 is a cross-sectional elevation view of another example of apackaged electronic device in which multiple layers of electricalconductors are provided.

FIG. 7 is a cross-sectional elevation view of another example of apackaged electronic device in which openings to exposed areas ofelectrical conductors are provided on a side of the electricalconductors opposite to a die of the packaged electronic device.

DETAILED DESCRIPTION

For convenience, the term “implantable” as used herein is intended toencompass not only devices that may be installed and operated within aliving organism but also devices that may be attached to the outer skinof a living organism.

As used herein, the term “biocompatible,” in the context of a materialor device intended for in vivo implantation, generally means that thematerial or device after implantation will not have toxic or otherwiseinjurious effects at the local level (e.g., surrounding tissue) orsystemic level. “Biocompatible” also means structurally or mechanicallycompatible, in that the material or device after implantation is able toperform its intended function or provide its intended therapeuticeffects while minimizing adverse physical effects in surrounding tissue.Generally, a structurally or mechanically compatible material or deviceis sufficiently flexible so as to be conformable with the surroundingtissue.

In general, terms such as “communicate” and “in . . . communicationwith” (for example, a first component “communicates with” or “is incommunication with” a second component) are used herein to indicate astructural, functional, mechanical, electrical, signal, optical,magnetic, electromagnetic, ionic or fluidic relationship between two ormore components or elements. As such, the fact that one component issaid to communicate with a second component is not intended to excludethe possibility that additional components may be present between,and/or operatively associated or engaged with, the first and secondcomponents.

For purposes of the present disclosure, it will be understood that whena given layer (or film, region, substrate, component, device, structure,or the like) is referred to as being “on” or “over” another layer, or“bonded to” another layer, that given layer may be directly or actuallyon (or over, or bonded to) the other layer or, alternatively,intervening layers (e.g., buffer layers, transition layers, interlayers,sacrificial layers, etch-stop layers, masks, electrodes, interconnects,contacts, or the like) may also be present. A given layer that is“directly on” another layer at the juncture between the two layers, or“bonded directly to” another layer, means that no intervening layer ispresent, unless otherwise indicated. It will also be understood thatwhen a given layer is referred to as being “on” (or “over”) anotherlayer, or “bonded to” another layer, that given layer may cover theentire surface of the other layer or only a portion of the other layer.It will be further understood that terms such as “formed on,” “disposedon,” “bonded to” and the like are not intended to introduce anylimitations relating to particular methods of material transport,deposition, fabrication, surface treatment, or physical, chemical, orionic bonding or interaction, unless otherwise indicated.

As used herein, the term “die” refers to a piece or body of material onand/or into which electronic (or electrical) circuitry (i.e., diecircuitry) has been fabricated. Typically in the context of integratedcircuits, as appreciated by persons skilled in the art, several copiesof the same integrated circuit may be fabricated on a relative largewafer or substrate of semiconducting material. The semiconducting waferis then separated into several pieces, with each resulting piece being adie containing a respective one of the circuits. In the context of thepresent disclosure, however, the material comprising the die, or in thecase of dicing operations the larger substrate from which the die isformed, is not limited to being a semiconducting material.

FIGS. 1A and 1B illustrate an example of a packaged electronic device150 fabricated in accordance with any of the implementations taught inthe present disclosure. FIG. 1A is a cross-sectional elevation view ofthe packaged electronic device 150, while FIG. 1B is a correspondingplan view of the packaged electronic device 150 with certain features orcomponents removed for illustrative purposes. The cross-section of FIG.1A is taken along line 140 of FIG. 1B.

Referring to FIG. 1A, the packaged electronic device 150 includes a die102 integrally bonded to a flexible circuit structure 170 (consisting ofstructural layers 106, 112, and electrical conductors 110) by means ofan attachment layer 114. The flexible circuit structure 170 includeselectrical conductors 110 disposed on or embedded in a first structurallayer 106. The die 102 may include one or more active and/or passivecircuitry devices (die circuitries) 104 in signal communication withelectrical contacts provided on or in the die 102. The die 102 hasthrough-wafer-interconnect structures 108 which provide signalcommunication between the circuitry devices 104 formed on one side ofthe die 102 and the embedded electrical conductors 110 of the flexiblecircuit structure 170 bonded to the opposing side of the die 102. Thetop side and all lateral sides of the die 102, as well as the electricalconductors 110, are encapsulated by a flexible insulating film (orsecond structural layer) 112 such that the die 102 and the electricalconductors 110 are completely embedded within flexible material (i.e.,the first structural layer 106 and the second structural layer 112 inthe present example). An additional conformal protective andbiocompatible barrier layer 118 may be applied to cover all exposedsurfaces of the article. Openings 116 may be patterned in the protectivebarrier layer 118 and in the flexible insulating film 112 to exposeportions of the electrical conductors 110. These openings 116 enablesignal communication between the device 150 and the bio-physiologicalenvironment. Alternately, these openings 116 may be filled withelectrical interconnects or contacts, or occupied by wires, as needed toenable signal communication between the circuitry devices 104 andanother electronic device 160 via the electrical conductors 110. In theillustrated example, the electrical conductors 110 include respectivefirst ends 166 with which the interconnect structures 108 are in signalcommunication and respective second ends 168 with which the conductivestructures of the openings 116 are in signal communication. In thiscontext, the term “end” is not limited to an extreme boundary or edge ofany electrical conductor 110 but instead more generally designates anend region of the electrical conductor 110. That is, the first ends 166may be end regions proximal to the die 102 and remote from the otherelectronic device 160, while the second ends 168 may be end regionsproximal to the other electronic device 160 and remote from the die 102.

As further shown in FIGS. 1A and 1B, in some implementations theflexible circuit structure 170 may be appreciably long in one dimensionso as to define a flexible cable portion 120 capable of carrying signalsfrom the circuitry devices 104 to the other electronic device 160, whichmay thus be remotely situated relative to the circuitry devices 104. Theremote device 160 may be any device that would benefit from cooperationwith the die 102 on the packaged electronic device 150. The remotedevice 160 may be placed in signal communication with the circuitrydevices 104 via any suitable electrical connection made through theopenings 116 over the electrical conductors 110.

As non-limiting examples, the remote device 160 may be anelectro-stimulation device configured for neurostimulation (for exampleretinal or cranial prosthesis), muscular stimulation, or the like. Insuch a case the remote device 160 may, for example, include an array ofelectrodes 162 disposed on a suitable substrate 164. Other examples ofremote devices include, but are not limited to, various sensors ordetectors (including sensors or detectors that acquire measurements of adesired property such as electrical signals, temperature, pressure,etc., provide an indication of a certain condition such as gasdetection, biosensors, chemical sensors, etc.), optical devices, imagecapturing devices, radio-frequency (RF) communication devices,electro-mechanical devices, micro-electro-mechanical systems (MEMS),labs-on-a-chip, etc. The packaged electronic device 150 in combinationwith the remote device 160 may comprise a biocompatible electronicassembly (or device, apparatus, system, instrument, etc.) suitable forin vivo implantation. The flexibility of the cable portion 120 likewiseprovides significant flexibility in the design, function and operationof such an implantable electronic assembly. For instance, in the case ofa retinal prosthesis, both the packaged electronic device 150 and theremote device 160 may be implanted within the eye. Alternatively, theremote device 160 may be situated outside the eye while neverthelessremaining tethered to the packaged electronic device 150 via the cableportion 120 of the flexible circuit structure 170, which may extendthrough the outer tissue of the eye by means of a surgical incision.Likewise, in the case of a brain signal recording device, both thepacked electronic device 150 and the remote sensor 160 may be implantedin the brain. Alternatively, the remote sensor 160 may be implanted andthe electronic device 150 remains outside the brain fixed to the skullbut tethered to the sensor 160 via a cable portion 120 of the flexiblecircuit structure 170.

The resulting article illustrated in FIGS. 1A and 1B is a fullyencapsulated packaged electronic device 150. The total thickness of thecable portion 120 may range, for example, from 5 μm to 200 μm. The totalthickness of the encapsulated electronic device 150 including the die102 may range, for example, from 15 μm to 250 μm. In advantageousimplementations, the die 102 itself is flexible and thereby impartsadditional flexibility to the packaged electronic device 150. The degreeof flexibility of the die 102 will depend on its composition andthickness. In a typical example, die 102 is a semiconducting materialsuch as, for example, silicon, a semiconducting silicon-inclusivecompound or alloy, a Group III-V compound, a Group II-VI compound, orany other semiconducting material that is flexible in the range ofthicknesses contemplated for the present teachings. As examples, thethickness of the die 102 may range from 10 μm to 50 μm, or moretypically from 10 μm to 30 μm. In one specific example, the die 102 issilicon and has a thickness of about 23 μm to 25 μm and a planar area of5 mm by 5 mm. More generally, the die 102 may be a semiconductor,compound semiconductor, metalloid (or metalloid-inclusive compound oralloy), ceramic, glass, polymer, or metal (or metal-inclusive compoundor alloy). In some implementations, the die 102 is thin enough (andhence flexible enough) such that when the packaged electronic device 150is rolled end to end into a cylinder (e.g., when the packaged electronicdevice 150 shown in FIG. 1A is bent such that the left end meets theright end), the outermost radius of the packaged electronic device 150is 1 mm or less.

The packaged electronic devices fabricated according to theimplementations described herein are expected to perform well during invitro testing, protect the underlying conductors and microelectrodes inisotonic saline solutions at 37 degrees Celsius (human body temperature)for several years and at the same time exhibit good biocompatibility.Accordingly, as noted throughout the present disclosure, the electronicdevices taught herein are useful not only in more general orconventional applications but also in applications entailingenvironmental isolation or in vivo implantation.

FIGS. 2A-2J illustrate an example of a method for fabricating a packagedelectronic device that includes a die integrated with a flexible circuitstructure in accordance with the present teachings, such as, forexample, the packaged electronic device 150 illustrated in FIGS. 1A and1B.

Referring to FIG. 2A, a rigid sacrificial substrate or wafer 202 isprovided. The substrate 202 may have any suitable composition andthickness, so long as the substrate 202 is rigid enough to serve as afree-standing substrate capable of supporting the building of a flexiblecircuit structure as described below. Moreover, the substrate 202 mustbe compatible with the process steps taken to build the flexible circuitstructure. For instance, in cases where the building of the flexiblecircuit structure entails thermal curing, the substrate 202 must becapable of withstanding such thermal curing. As other examples, againdepending on the process undertaken for fabricating the flexible circuitstructure, the substrate 202 may also need to be compatible withdeveloper chemicals, etchants, etc. The substrate 202 may beelectrically conductive, semiconducting, or insulating. The substrate202 may be an elemental metalloid or semiconductor (e.g., silicon), asemiconductor compound or alloy, a glass, a ceramic, a dielectric, apolymer, or a metal. In one non-limiting example, the substrate 202 is asilicon wafer having a thickness (in the vertical direction from theperspective of FIG. 2A) of 250 μm. The substrate 202 includes a firstsurface 204 and an opposing second surface 206, the thickness of thesubstrate 202 being generally defined as extending between and includingthe first surface 204 and the second surface 206.

In this context, terms such as “first” and “second” are arbitrary as nolimitations are placed on a particular orientation of the substrate 202or any other component of the packaged electronic device beingdescribed. For instance, either the first surface 204 or the secondsurface 206 could be a bottom surface, an inside surface, a top surface,an outside surface, etc. Moreover, it will be understood that theillustrated substrate 202 may represent a portion or section of a fullwafer of substrate material. Accordingly, persons skilled in the artwill appreciate that FIGS. 2A-2J may be representative of the use of alarge wafer or substrate 202 and the simultaneous microfabrication ofseveral packaged electronic devices.

Referring to FIG. 2B, a sacrificial release film 208 is formed on thefirst surface 204 of the substrate 202. The release film 208 may haveany composition suitable for serving as a sacrificial material. Asnon-limiting examples, the release film 208 may be a metal (e.g., Al,Cr, etc.), an oxide (e.g., SiO₂), a nitride (e.g., Si₃N₄), or a polymer.The release film 208 may formed by any technique suitable for itscomposition. As an example, in the case of a metal release film 208 suchas Al or Cr, the release film 208 may be formed by sputter depositionaccording to known techniques. No specific limitation is placed on thethickness of the release film 208.

Continuing with FIG. 2B, a first structural layer 210 is formed on thesacrificial release film 208 by any technique suitable for thecomposition of the first structural layer 210, and which results in thefirst structural layer 210 covering the sacrificial release film 208 inan area that defines the overall footprint of the final packagedelectronic device. The first structural layer 210 may have any suitableelectrically insulating composition for this purpose. In addition, theas-deposited material of the first structural layer 210 should beflexible. A few non-limiting examples include polymers such as polyimide(which includes copolymers of polyimide and blends of polyimide),polyparaxylylene (e.g., the class of Parylenes), liquid-crystal polymers(LCPs), and benzocyclobutene (BCB). The polymer may or may not bephoto-definable. In advantageous implementations, the first structurallayer 210 is a polymer of the type that can be deposited by a spin-oncoating process although other material-additive processes such as dipcoating may be suitable. In further advantageous implementations, thefirst structural layer 210 is a polymer that includes an adhesionpromoter, one specific example being a photo-definable polyimideprecursor solution such as commercially available from HD Microsystems,Parlin, N.J. and designated Pyralin® PI2723 or also commerciallyavailable from Fujifilm Electronic Materials U.S.A. Inc., Queen Creek,Ariz. and designated Durimide 7020. The adhesion promoter may be of thetype designed to provide covalent bonds to the surface of the componentto be subsequently placed or deposited on the first structural layer 210such as an electrically conductive layer, a die, another structurallayer utilized for adhesion or encapsulation, etc. Generally, anadhesion promoter may be selected for use in conjunction with a varietyof compositions of the surface of the sacrificial release film 208,including silicon, glass, quartz, ceramics, metals, inorganic oxides,inorganic nitrides, and polyimides. The portion of the first structurallayer 210 that covers the release film 208 may have any suitablethickness. As an example, the thickness of the first structural layer210 may range from 2 μm to 100 μm. In one specific example, thethickness of the first structural layer 210 is 10 μm.

As an alternative or in addition to the first structural layer 210including a built-in adhesion promoter, an adhesion promoter may beapplied as an external layer (or film, coating, etc., not specificallyshown) may be applied on a surface of the first structural layer 210prior to depositing a component (e.g., an electrically conductive layer,a die, another structural layer utilized for adhesion or encapsulation,etc.) on the first structural layer 210 to enhance bonding between thatcomponent and the first structural layer 210. The external adhesionpromoter may have any composition suitable for this purpose, one exampleof which is a silanizing agent. The external adhesion promoter may beapplied by spin-on coating, spray-on coating, dip coating, or the like.The external adhesion promoter may be in the nature of a surfacetreatment. In addition to wet surface treatments, a dry surfacetreatment such as exposure to a plasma beam may be performed for surfacefunctionalization, as appreciated by persons skilled in the art.

Referring to FIG. 2C, electrical conductors (e.g., traces) 212 areformed so as to extend along at least a portion of the first structurallayer 210. In a typical implementation contemplated by the presentteachings, the material utilized for forming the electrical conductors212 is a metal or metal alloy. The metal or metal alloy may be depositedby any suitable technique, such as a vacuum deposition technique, forinstance a physical vapor deposition (PVD) technique such as sputtering.In some implementations, two or more layers of different metals aredeposited to form the electrical conductors 212. As an example, themetallization may consist of first depositing Cr followed by depositingAu, where Cr may serve primarily as an adhesion layer. The portion ofthe metal film that covers the first structural layer 210 may have anysuitable thickness. In one specific example entailing the deposition ofa bilayer of Cr and Au, the thickness of the Cr is 20 nm and thethickness of the Au is 200 nm. As one non-limiting example of formingthe electrical conductors 212, the deposited metal film is patterned byutilizing a photoresist etch mask (e.g., Shipley 1813, commerciallyavailable from Shipley Co. Inc., Freeport, N.Y.) and chemical wetetchants to define the electrical conductors 212.

Referring to FIG. 2D, another structural layer, which will be referredto herein as an attachment layer 214, is deposited so as to conformallycover the electrical conductors 212 as well as all exposed surfaces ofthe first structural layer 210 and the sacrificial release film 208. Theattachment layer 214 may have any suitable electrical insulativecomposition for this purpose, should be flexible, and should adhere wellto both the first structural layer 210 and the die to be attached aswill be explained below. The attachment layer 214 may be deposited byany technique suitable for its composition and have any suitablethickness. The first structural layer 210 may be cured, such as bythermal curing (heat application), prior to depositing the attachmentlayer 214. In one implementation, the composition of the attachmentlayer 214 is the same or similar as that of the first structural layer210 (e.g., polyimide). In some implementations, the thickness of theattachment layer 214 (above a given surface, such as that of the firststructural layer 210) ranges from 0.5 μm to 5 μm, in otherimplementations from 1 μm to 4 μm. In some specific examples, thethickness is 2 μm or 3 μm. More generally, the thickness of theattachment layer 214 should be sufficient for providing a robust bondbetween the electrical conductors 212 and first structural layer 210 andthe die to be subsequently placed thereon, while not impairing theflexibility of the electronic device being fabricated and notappreciably adding to the overall thickness of the electronic device. Abuilt-in adhesion promoter, external adhesion promoter or surfacetreatment may be employed as described above to facilitate or enhancethis bond. It will be understood that a term such as “adhere” or “bond”when used in the context of the attachment layer 214 indicates that theattachment layer 214 promote or enhances attachment of the die to theunderlying surface (i.e., the first structural layer 210 in this case),in that the attachment layer 214 is still tacky when applied and whenthe die is subsequently placed on the attachment layer 214 and alignedproperly with the underlying electrical conductors 212. That is, theattachment layer 214 is not the same as an adhesive dry film, liquidadhesive, thermosetting adhesive, pressure-sensitive adhesive, underfillmaterial, or the like. These latter, conventional materials aretypically much thicker and function solely as adhesives, glues orspace-filling materials.

Referring to FIG. 2E, a die 216 is aligned and attached to theattachment layer 214 over a predefined area of the electrical conductors212. At this time, the attachment layer 214 is not yet cured or may beonly partially cured so as to provide tackiness for the die 216. The die216 includes die circuitry 219 (e.g., one or more electrical circuits ordevices) formed at (on and/or into) one of the die 216 surfaces (the topsurface as oriented in FIG. 2E) by any suitable technique. The specifictechnique selected may depend on a number of factors, including thefeatures and/or functions of the die circuitry 219. The die circuitry219 may include active attributes (e.g., transistors, p-n junctions,active sensors, etc.) and/or passive attributes (e.g., resistors,capacitors, inductors, thermistors, conductive leads, ground planes,passive sensors, etc.). Additionally, the die 216 includes one or morethrough-wafer-holes 218 which extend between the two surfaces of the die216. The die 216 is aligned and placed on the attachment layer 214 insuch a way that the through-wafer-holes 218 are directly above theappropriate electrical conductors 212. This alignment and placement maybe by any appropriate manual or automated means. The composition andthickness of the die 216 may be as described earlier in this disclosure.

The through-wafer-holes 218, which extend through the entire thicknessof the die 216, may be formed by any means suitable for the compositionof the die 216 and utilized in precision microfabrication, such as forexample mechanical drilling (typically with the use of a diamond drillbit), laser drilling, ultrasonic milling, chemical etching, or dryetching. In the case of a silicon wafer or the like, deep reactive ionetching or DRIE (e.g., the Bosch process) may be utilized. The diameterof the through-wafer-holes 218 may range from 4 μm to 100 μm. The pitchof (or spacing between) the through-wafer-holes 218 may range from 10 μmto 1000 μm. In one specific example, the diameter of thethrough-wafer-holes 218 is 50 μm and the pitch of thethrough-wafer-holes 218 is 150 μm. The through-wafer-holes 218 may beformed either prior to or subsequent to die 216 placement onto theattachment layer 214. The case illustrated is that of thethrough-wafer-holes 218 formed prior to die 216 placement. The sidewallsof the through-wafer-holes 218 may be covered with a conformal layer ofinsulation (not shown) to electrically insulate the bulk material of thedie 216 from subsequently fabricated electrically conductiveinterconnects. Any suitable insulating material that can be applied byconformal deposition may be utilized, a few examples being oxides suchas SiO₂, nitrides such as Si₃N₄, and the class of Parylenes. Anydeposition method suitable for the composition of the insulating layermay be employed. One typical example is a vacuum deposition techniquesuch as chemical vapor deposition (CVD).

Referring to FIG. 2F, the areas of the attachment layer 214 that are notdirectly covered by the die 216, including the areas of the attachmentlayer 214 exposed by the through-wafer-holes 218, are removed by anysuitable means. In one non-limiting example, this removal isaccomplished by reactive ion etching where the die 216 acts as aphysical mask to protect the portion of the attachment layer 214directly under the die 216.

Referring to FIG. 2G, electrically conductive interconnects 220 aredeposited in the through-wafer-holes 218 to electrically connect the diecircuitry 219 to the electrical conductors 212. These electricalconductive interconnects 220 may completely fill, partially fill, oronly coat the sidewalls of the through-wafer-holes 218 with therequirement being a robust electrical connection between the diecircuitry 219 and the electrical conductors 212 to enable reliablesignal communication. The electrically conductive interconnects 220 maybe formed by any suitable means including, but not limited to, physicalvapor deposition (PVD), electroplating, screen-printing, etc.

Referring to FIG. 2H, a second structural layer 222 is conformallydeposited so as to encapsulate the die 216 and the electrical conductors212 while leaving openings 224 that define electrical contact areas onthe electrical conductors 212. The composition of the second structurallayer 222 may be the same or different from that of the first structurallayer 210 and/or the attachment layer 214. The second structural layer222 may be deposited by any technique suitable for its composition. Insome implementations, the second structural layer 222 is polyimide. Thesecond structural layer 222 may have any suitable thickness, butgenerally must be thick enough to form an adequately conformal layer andhence may depend in part on the thickness of the die 216. As an example,the thickness of the second structural layer 222 (over a given surfacesuch as that of the die 216) may range from 2 μm to 100 μm one specificexample, the thickness of the second structural layer 222 is 10 μm. Thesecond structural layer 222 may include a built-in adhesion promoter, oralternatively an external adhesion promoter or surface treatment may beapplied as noted above, to facilitate or enhance conformal coverage ofthe underlying surfaces or components on which the second structurallayer 222 is deposited. To render full encapsulation of the die 216 andthe electrical conductors 212, portions of the second structural layer222 may be directly deposited on corresponding portions of the firststructural layer 210.

Referring to FIG. 2I, the sacrificial release film 208 (FIGS. 2B-2H) isremoved by any means suitable for the composition of the release film208, therefore separating the first structural layer 210 from thesubstrate 202 (FIGS. 2A-2H). This removes the packaged electronic devicebeing built from the rigid substrate 202 (FIGS. 2A-2H) that was used forhandling and support during the prior processing steps described above.

Referring to FIG. 2J, to provide enhanced protection, an additionalbarrier coating 226 (film, layer, etc.) may be optionally deposited ontothe first structural layer 210 and the second structural layer 222including the sidewalls of these layers. The barrier coating 226 may bepatterned so as to maintain the openings 224 defined by the secondstructural layer 222. The barrier coating 226 may have any suitablecomposition utilized in the packaging of electronics. In implementationswhere the packaged electronic device described herein is intended for invivo or in vitro implantation and operation, the barrier coating 226should be biocompatible. In some implementations, the barrier coating226 has a diamond-like carbon (DLC) inclusive composition, which may beconformally deposited by, for example, plasma-enhanced chemical vapordeposition (PECVD) utilizing a known precursor material such as, forexample, an appropriate hydrocarbon such as methane. Patterning may beaccomplished by, for example, a standard photoresist lift-off procedure.The barrier coating 226 may have any suitable thickness. In one specificexample, the thickness of the barrier coating 226 is 300 nm. The surfaceproperties of the DLC films utilized in this example can be engineeredto yield hydrophilic or hydrophobic surface properties to improvebiocompatibility, such as by adding appropriate dopants (e.g., oxygen,fluorine, etc.) or by performing a surface treatment (e.g., surfacefunctionalization) such as plasma or wet treatment. The DLC filmsexhibit excellent adhesion to most plastic substrates and metals, can beeasily patterned, and exhibit low moisture and oxygen permeabilities.Some examples of suitable DLC-inclusive films are described in U.S.Patent App. Pub. No. US 2002/0172938, the entirety of which isincorporated herein by reference. Other examples of the barrier coating226 include, but are not limited to, a Parylene, amorphous SiO₂, andamorphous Si₃N₄ or combinations of the foregoing. Additionaldescriptions of barrier coatings 226 are provided below.

Depending on the specific design or purpose of the end-use article, theopenings 224 (FIG. 2J) to the electrical conductors 212 may be filledwith an electrically conductive material to provide electrode contactssuch as, for example, bond pads (not shown). As one example, theopenings 224 may be filled with a Pt—Ir alloy by sputter-deposition.

In implementations where the outermost surfaces of the packagedelectronic device 250 (e.g., the barrier layer 226 and/or the firststructural layer 210 and the second structural layer 222) are composedof biocompatible materials, the resulting electronic device 250 issuitable for in vivo or in vitro implantation and operation. Moreover,it can be seen that the die 216 and the first structural layer 210 arefully integrated with each other as a unitary electronic device 250 viathe thin attachment layer 214, which as described above may becharacterized as an additional structural layer or an extension of thefirst structural layer 210 (particularly when the attachment layer 214and the first structural layer 210 have the same composition) andprovides tackiness at a stage of fabrication when the first structurallayer 210 may no longer provide sufficient tackiness to ensure goodbonding with the die 216. Thus, there is no separation of the die 216and the first structural layer 210 by solder bumps, layers of underfillmaterials, or other features conventionally required for spacers,electrical interconnects, structural rigidity, and the like. As aconsequence, intimate contact is formed between the die 216 and thefirst structural layer 210 with improved seals for all points ofelectrical contact, improved biocompatibility, and increased mechanicalstability of the areas of contact between the die 216 and the firststructural layer 210. Hence, many of the potentially weak connectionpoints in this type of device are eliminated and the electricalcomponents of the die 216 and the electrical conductors 212 areintrinsically encapsulated by the microfabrication process.

FIG. 3 is a planar view of a wafer 302 as an example of a substrate onwhich a plurality of flexible circuit structures 350 may be fabricated.The respective footprints of the flexible circuit structures 350 areindicated by dotted lines. Fourteen flexible circuit structures 350 areillustrated by example. The number of flexible circuit structures 350that may be built on the surface of the wafer 302 may be more or lessthan fourteen, depending on the size of the wafer 302 and the size ofthe flexible circuit structures 350. Die areas 308 depicted in FIG. 3represent the footprint of the die circuitries and accompanyingelectrical contacts, terminations of vertical interconnects, or the likeas described above in conjunction with the implementations illustratedin FIGS. 1A-2J. A plurality of electrical conductors or traces 318 areembedded within the insulating structural material utilized in buildingthe flexible circuit structures 350 as described above, and aresufficiently isolated from each other so as to avoid cross-talk. Foreach flexible circuit structure 350, five electrical conductors 318 areillustrated by example—more or less may be provided. The electricalconductors 318 provide signal communication between the electricalcontacts of the die areas 308 and corresponding electrode sites or bondpads 326 formed remotely from the die areas 308. Depending on the designand purpose of the electronic devices being fabricated, the electrodesites or bond pads 326 may be physically connected or wirelesslyinterfaced with other electronic devices. As but one non-limitingexample, the electrode sites or bond pads 326 may communicate with anelectrode array utilized for in vivo/in vitro neurostimulation. FIG. 3also illustrates that the lengths of the flexible circuit structures 350generally in the direction of the electrical conductors 318 may be largerelative to their widths. Accordingly, the flexible circuit structures350 may serve as flexible ribbon cables in various implementations.

Referring to FIG. 4, it is possible to include multiple die on a singlepackaged electronic device 450. In the illustrated example, a planar(i.e., side by side) arrangement of two discrete die 422 and 432 arebonded to a first structural layer 406 by means of attachment layers 414and 434 and electrically connected to the electrical conductors 410 bymeans of respective through-wafer-interconnects 428 and 438 between diecircuitry 424 and 434 and the electrical conductors 410. The second die432 communicates with one or more electrical conductors 410 via one ormore interconnects 438 positioned at intermediate locations of theelectrical conductors 410 between the first ends and the second ends ofthe electrical conductors 410. This may be accomplished by using theprocess steps described in FIGS. 2A-2J where more than one die arealigned and attached in the steps associated with FIG. 2E. A secondstructural layer 412 completes the encapsulation in the manner describedabove, and a barrier film or coating 418 may optionally be provided. Thedie 422 and 432 may communicate with one another or with any remotelysituated device (not shown) as described above by means of theelectrical conductors 410 and corresponding openings 416. The electricalconductors 410 may extend along a flexible cable portion 420 in alongitudinal direction (i.e., the direction generally from the die 422and 432 to the openings 416). While FIG. 4 illustrates two discrete die422 and 432, it is understood that any advantageous number of die can beincluded in the packaged electronic device 450. While FIG. 4 illustratesa planar arrangement of multiple die along the longitudinal direction,multiple die may also be arranged along the orthogonal lateral direction(i.e., the direction into the drawing sheet of FIG. 4), or in atwo-dimensional array along both the longitudinal and lateraldirections.

FIG. 5 illustrates another example of providing multiple die in a singlepackaged electronic device 550. In the illustrated example, a verticalarrangement of three discrete die 502, 522, 532 and respective diecircuitry 504, 526, 536 are provided. Each successive die in thevertical stack is attached to the die immediately below it. The firstdie 502 is attached to the first structural layer 506 and the electricalconductors 510 by means of an attachment layer 514, and the diecircuitry 504 on this first die 502 is in electrical contact with theelectrical conductors 510 by means of through-wafer interconnects 508 asdescribed above. Additional die are “stacked” onto this first die 502prior to the deposition of a second structural layer 512. In processsteps similar to those described above, a second attachment layer 524may be deposited on the first die 502 and a second die 522 aligned andattached to the first die 502. Through-wafer-interconnects 528 in thesecond die 522 enable signal communication between the die circuitry 526on the second die 522 and the die circuitry 504 on the first die 502.Similarly, a third attachment layer 534 may be deposited on the seconddie 522, a third die 532 aligned and attached to the second die 522, andthrough-wafer-interconnects 538 in the third die 532 manufactured toenable signal communication between the die circuitry 536 on the thirddie 532 and the die circuitry 526 on the second die 522. Finally thesecond structural layer 512 is deposited and processing continues asdescribed in FIGS. 2H-2J, with the optional addition of a barrier film518. As in other implementations described above, the electricalconductors 510 may be interfaced with a remote device via openings 516,and may be extended along a flexible cable portion 520. While three die502, 522, 532 are illustrated in FIG. 5, the process could be limited totwo die or continued with additional stacked die.

The inclusion of multiple die on a single packaged electronic deviceoffers several advantages. One advantage is that each die may beconfigured to handle different functions to improve the performanceand/or efficiency of the device. For example, one die might containdigital circuitry while another die might contain analog circuitryallowing for each type of circuitry to be fabricated by a differenttargeted process. Another advantage is that redundancy could be builtinto a critical device where two or more identical die are included thatcould be enabled/disabled remotely in the case that one of the diefailed for any reason during the lifetime of the device. Yet anotheradvantage is that additional circuitry can be included withoutincreasing individual die size which could lead to lower die yield andthus increased cost.

Multiple die may be included on a single packaged electronic device notonly in a panar arrangement as illustrated in FIG. 4, but also in avertical arrangement as illustrated in FIG. 5. The three-dimensional(3D) integration or “chip stacking” shown in FIG. 5 represents animproved method for vertically aligning and bonding multiple dies. Thesemiconductor industry is employing 3D integration technologies toachieve higher performance (faster signal processing, lower powerconsumption), smaller device size and much higher I/O count, all ofwhich may be facilitated through the use of through-wafer interconnects.Conventionally, microelectronics are fabricated in a traditional 2Dsurface-mount or flip-chip approach. Device size is dictated by thenumber and physical dimensions of the IC chips used, and is alsoimpacted by the discrete passive surface mount components provided.However, by stacking and interconnecting the various dies, one canexpect to get a dramatic decrease in the size (footprint area) andweight of the electronics, an important consideration for implantableneural prostheses and other electronic devices contemplated by thepresent teachings Vertical interconnects allow the opportunity to bondan active device to a passive component layer containing resistors,capacitors, inductances or power ground planes with a high density ofinterconnects. The possibility of integrating passive components such ascapacitors onto the stacked device and moving them off the flexsubstrate will reduce device size further and minimize reliabilityconcerns with these surface mounted devices.

FIG. 6 illustrates a packaged electronic device 650 that includemultiple layers or elevations of electrical conductors 610, 630, 640. Insome implementations, some of the electrical conductors 610, 630, 640may be arranged vertically while others are side by side in the lateraldirection (i.e., into the drawing sheet of FIG. 6). In otherimplementations, all of the electrical conductors 610, 630, 640 may bearranged vertically. Each layer of electrical conductor(s) 610, 630, 640is sandwiched between adjacent structural layers 606, 612, 622, 632 andconsequently spaced and electrically isolated from the other electricalconductors 610, 630, 640. A single die 602 and associated die circuitry604 may be provided and may be bonded to the internal structural layer622 by an attachment layer 614 as described above. The die circuitry 604may communicate with respective electrical conductors 610, 630, 640 viacorresponding interconnects 638, 628, 608. Alternatively, multiple diemay be provided as described above in conjunction with FIGS. 4 and 5,with selected die circuitries communicating with each other or withselected electrical conductors 610, 630, 640 or layers of electricalconductors 610, 630, 640 (i.e., one of more electrical conductors 610,630, 640 of the same level or elevation). The structural layers 606,612, 622, 632 may be patterned so as to provide vias in appropriatelocations whereby each electrical conductor provides signalcommunication between the die circuitry 604 and at least one electrodesite 616, 626, 636 (which may be placed in signal communication withanother device external to or remote from the die circuitry).Alternately, the internal structural layers 612, 622 may be patterned soas to provide signal communication between electrical conductors 610,630, 640 on different layers. While three layers of electricalconductors 610, 630, 640 are illustrated in FIG. 6, it is understoodthat this is not limiting and that two layers of electrical conductorsor four or more layers of electrical conductors may be included.Encapsulation is completed by a second structural layer 632 with orwithout an additional barrier layer 618, as described above. Theelectrical conductors 610, 630, 640 may be extended along a flexiblecable portion 620 as described above.

FIG. 7 illustrates another example of a package electronic device 750. Adie 702 includes die circuitry 704 and is bonded to a flexible circuitstructure by an intermediate structural layer (or attachment layer) 714.The flexible circuit structure includes a first structural layer 706 onor in which electrical conductors 710 are disposed. The die circuitry704 communicates with the electrical conductors 710 via verticalinterconnects 708 that extend through the die 702 and the intermediatestructural layer 714. The electrical conductors may extend along aflexible cable portion 720. The die 702 and the electrical conductors710 are encapsulated by the first structural layer 706 and a secondstructural layer 712, and an additional barrier layer 718 may optionallybe provided. In this example, openings 716 defining respective exposedareas on the electrical conductors 710 are patterned in the firststructural layer 706 rather than the second structural layer 712 as wasdescribed in FIGS. 2A-2J. This results in the openings 716 and the die702 being on the opposite sides of the electrical conductors 710, whichmay be advantageous in certain implementations. The process flowrequired to produce this implementation is similar to the process flowdescribed above, the modifications being readily apparent to thoseskilled in the art in view of the foregoing disclosure. Additionally(not shown), openings to the electrical conductors 710 may be patternedin both the first structural layer 706 and the second structural layer712, resulting in contact to these electrical conductors from both sidesof the packaged electronic device 750.

As described above, barrier coatings such as the barrier coatings 118,226, 418, 518, 618 and 718 shown in the Figures may be provided toimpart to or enhance hermetic, insulating and/or biocompatibleproperties of the substrates to which the barrier coatings are applied,such as the above-described flexible structural layers that typicallyare polymers such as, for example, chemically cross-linked polymers suchas polyimides. The composition of the barrier coating and/or the mannerin which it is surface-treated may determine whether the barrier coatingis biocompatible in a given implanted application (e.g., a particular invivo site). For a given application, biocompatibility may be indicatedby whether the barrier coating is hydrophilic or hydrophobic, or has anaffinity or non-affinity for certain specific biomaterials (e.g.,biomolecules, blood, tissues, tissue fluids, etc.), or is adsorptive ornon-adsorptive of certain specific biomaterials. An adsorbed proteinlayer mediates the subsequent biochemical and cellular events at thesurface of the implant, which may determine the biocompatibility of theimplant. For example, when considering compatibility with blood, theamount and type of protein that adsorbs onto the surface of an implanteddevice may either trigger or prevent coagulation and/or thrombosis.Three of the most abundant proteins found in blood plasma arefibrinogen, albumin and immunoglobin G (IgG). Albumin adsorbed onto asurface has been observed to reduce subsequent platelet deposition.Brash, J. L. and Uniyal, S., “Dependence of albumin-fibrogen simple andcompetitive adsorption on surface properties of biomaterials,” Journalof Polymer Science 1979 (66), which is incorporated by reference hereinin its entirety. On the other hand, fibrinogen is thought to play acentral role in blood coagulation and support platelet adhesion andaggregation through binding to glycoprotein (GP) IIb-IIIc integrinreceptors. Slack, S. M. and Horbett, T. A., “The Vroman Effect: ACritical Review,” ACS Symposium Series No. 602, American ChemicalSociety, 1995, which is incorporated by reference herein in itsentirety. Therefore, surfaces that have a high affinity for albumin maybe more biocompatible than surfaces with a high affinity for fibrinogen.As another example, cell adhesion may be greater on hydrophilicsubstrates than on hydrophobic substrates. Van Wadrem, A. H. Hogt, J.Bengeling, J. Feigen, A. Bantjes, J. P. Detmers, and W. G. Van Akan,Biomaterials, 8, (1987), 323, which is incorporated by reference hereinin its entirety.

In some implementations, the barrier coating is a gas plasma-depositedpolymer. Gas plasma deposited polymers may be modified with various gasplasma treatments using oxygen or nitrogen-containing gases to result insurfaces with desired terminating functional groups. The surface of thegas plasma polymer may be modified with different functionalities andsurface energies to provide a desired adsorption or non-adsorptioncharacteristic for biomolecules. W. R. Gombatz, and A. S. Hoffman, CRCCritical Reviews in Biocompatability, 4, (1987), 1, which isincorporated by reference herein in its entirety.

As described above, polyimide is an example of a substrate to which thebarrier coating may be applied. The polyimide layer may be formed inaccordance with a number of techniques. For example, in oneimplementation, a polyimide precursor may be applied to a substrate viaa suitable method such as, for example, spin-coating or spray-coating.Typically, the precursor is applied in the form of a solution andthereafter cured, after which the polyimide will have a desiredthickness. One example of a suitable polyimide precursor containspendant photoreactive side groups. Upon exposure to radiation (e.g.,ultraviolet (UV) radiation), the photoreactive endgroups undergo a freeradical polymerization to form a crosslinked polyimide precursor. Such aprocess typically results in a solubility difference between the exposedand unexposed regions of the coating. The unexposed regions can beremoved by employing a suitable technique, such as, for example,dissolution in a suitable solvent (e.g., developer). The remainingcrosslinked intermediates may be subsequently converted to fullyimidized polyimides by thermal cure. The cured polyimide may be anaromatic polyimide. In some implementations, the polyimide layerincludes from about 50 to about 60 percent carbon and from about 10 toabout 40 percent silicon.

A number of methods may be utilized to form the barrier coating on thepolyimide or other type of substrate. Examples of techniques include,without limitation, plasma enhanced chemical vapor deposition (PECVD),chemical vapor deposition (CVD), sputtering, evaporation, and otherdeposition techniques such as plating, dip coating, flow coating, spraycoating, or spin coating. In some implementations, the coating is formedout of a material using precursors from, for example, silanes, siloxanes(e.g., polysiloxanes), silazanes, hydrocarbons, various metal organics,titanates, or metal alkoxides, as well as combinations of any of theabove. Examples of precursors that may be employed include, withoutlimitation, tetramethylsilane, trimethylsilane, tetramethoxysilane,hexamethyl disilane, hexamethyl disiloxane, hexamethyl disilazane,methane, ethane, ethylene, tetraalkoxy titanates, etc, as well ascombinations thereof. In general, oxides, carbides, and nitrides using anumber of metal organic precursors can be employed, along with oxygen,hydrocarbon, and nitrogen-containing gases respectively. The precursormay have low silicon content.

In some implementations, a PECVD process may be employed utilizing anyof the above-mentioned precursors (typically in the form of feed gas)introduced with or without argon or other inert gas and energizing thesematerials into a plasma by direct current, radio frequency, microwave,enhanced plasmas or by hollow cathode magnetron energy sources. Theenergized precursor (with or without energized argon or other inert gas)is promoted into an excited state, producing at least one of ionicfragments, free radicals, atoms, molecules, and mixtures thereof, in anexcited state which bombard and reconstruct on a base layer to produce acoating. In specific implementations, an alternating magnetic field isemployed to excite any of the precursors present in a reactor (e.g., avacuum chamber). Among other factors, the precursor and the processconditions are believed to influence the specific compositions andproperties of the coatings. The plasma enhanced chemical vapordeposition (PECVD) may be carried out at or slightly above roomtemperature. However, it will be appreciated that other temperatures canbe employed. For example, in one implementation, a higher substratetemperature in the range from about 300 to about 400° C. may be used fordeposition to attain specific properties such as lower incorporation ofhydrogen in the coatings for potentially improved mechanical andtemperature stability. Various pressures may be employed. For example,in some implementations, the pressure may range from about 10 mTorr toabout 1 atm (760 Torr). In a specific implementation, a pressure of 50mTorr is utilized.

Some examples of chemically crosslinked coatings suitable forimplementations described herein include amorphous Si—C—H coatings andamorphous silicon oxycarbide (Si—O—C—H). The Si—C—H coating may be anamorphous DLC material. Polymeric layers may include a chemicallycrosslinked material comprising elements selected from the groupconsisting of (1) M, O, C, H, and N, wherein M is a metal selected fromthe group consisting of silicon, titanium, tantalum, germanium, boron,zirconium, aluminum, hafnium and yttrium; (2) M, O, H, and N, wherein Mis defined above; (3) C; (4) O, C, H, and N; (5) M or C, and one of O,H, or N; and (6) C, H and O. Such coatings may be deposited on asubstrate using a variety of techniques, such as those described above.

Thus, the chemically crosslinked material may comprise a number ofcombination of elements. In some implementations, M is silicon which maybe present in combination with any one or more of the three elements: O,H, and N. In some implementations, the chemically crosslinked materialis applied by a PECVD and results in a crosslinked, amorphous matrix. Inone example, the material comprises from about 5 to about 30 percent byweight silicon, about 10 to about 60 percent carbon, about 10 to about60 percent hydrogen and trace amounts of oxygen, i.e., typically lessthan 3 percent. In another example, the chemically crosslinked materialcomprises from about 30 to about 60 percent carbon and from about 10 toabout 40 percent silicon. The coating may have a number of variousthicknesses. For example, the coating may have a thickness which is atleast a fraction of a monolayer thick. In this context, the term“fraction” of a monolayer refers to at least about 50 percent by area ofthe patterned surface regions where the coating is intended to bedeposited. In one example, the coating has a thickness ranging fromabout 200 nanometers to about 400 nanometers.

The coating may have a surface that is terminated with an electrophilicor nucleophilic functional group. Either the electrophilic or thenucleophilic functional group may be considered to be biocompatibledepending on the site or environment of the implantation and/or thenature (purpose, function, operation, etc.) of the device beingimplanted.

Thus, after forming a coating on the substrate or base layer, thesurface of the coating may be modified using various techniques. Forexample, in some implementations, an electronegative post-treatment of asurface of a coating may be a plasma treatment using various substancessuch as, without limitation, oxygen, ozone, water vapor, nitrogen oxide,fluorine, or fluorine gases/gas mixtures including fluorocarbons,fluorosilanes, or any other gas that would result in functionalitieshaving a negative polarity associated with them. The electronegativepost-treatment results in the surface being terminated with at least onenucleophilic functional group. The nucleophilic functional group mayinclude carbon, silicon, halogens, oxygen, hydrogen, nitrogen, sulfurand/or phosphorus. Another implementation encompasses a chemicalpost-treatment of the surface utilizing, as an example, perfluorinatedpolyethers, silanes terminated with electronegative functionalitites, orsimilar compounds such as those typically used for self assembledmonolayers (SAMs).

Any number of nucleophilic functional groups may be utilized. In thepresent context, the term “nucleophilic functional group” may be definedas a group capable of donating a pair of electrons to an electrophile.In various implementations, the nucleophilic functional group comprisesone or more elements selected from the group consisting of carbon,silicon, halogens, oxygen, hydrogen, nitrogen, sulfur, and phosphorus.Examples of electronegative surface sites include, without limitation,oxygenated or fluorinated functional groups or any other groupsdisplaying an electronegative polarity. Typically, the surface of thecoating material having nucleophilic functional groups attached theretois advantageous in that a build up of a negative polarity on the surfaceresults. Accordingly, materials having a negative charge (e.g.,biomolecules) are repelled, and thus the surface is non-adsorbing.

Alternatively, electropositive post treatment of the surface of thecoating may be carried out using a number of techniques including, butnot limited to, a plasma treatment employing hydrogen. Chemicalpost-treatments to obtain electropositive polarities may also beutilized if desired. The electropositive post-treatment results in thesurface of the coating being terminated with at least one electrophilicfunctional group. The electrophilic functional group can include carbon,hydrogen, nitrogen and silicon. Biomolecules may be adsorbed toelectrophilic functional group, including DNA, nucleic acids, proteins,enzymes, cells, viruses, and combinations thereof.

Any number of electrophilic functional groups may be utilized. In thepresent context, the term “electrophilic functional group” may bedefined as a functional group which has an electropositive polarity. Theelectrophilic functional group may comprise one or more elementsselected from the group consisting of carbon, hydrogen, nitrogen andsilicon. Examples of electrophilic functional groups include, withoutlimitation, any group capable of imparting a positive polarity to thecoating material including, for example, hydrogen-terminations, alkylgroups, and quarternary ammonium group molecules.

Advantageously, a number of materials may be adsorbed to theelectrophilic functional group. In the present context, the term“adsorbed” may be defined as increased adhesion of dissolved materials(e.g., biomolecules) to the surface of the chemically crosslinkedmaterial. The term “non-adsorbed” may be defined as decreased adhesionof dissolved materials (e.g., biomolecules) to the surface of thechemically crosslinked material. Not intending to be bound by theory, itis believed that a positive polarity is present on the coating surfacewhich electrostatically attracts and adsorbs negatively charged groups.Examples of negatively charged groups include, without limitation,electron-rich biomolecules or polyanions such as, for example, DNA,nucleic acids, proteins, enzymes, cells, viruses, and combinationsthereof. Examples of these materials are set forth in U.S. Pat. No.5,968,745 to Thorp et al., which is incorporated by reference herein inits entirety.

In some implementations, various portions of the surface of the coatingmay be terminated with at least one electrophilic functional group whileother surface portions may be terminated with at least one nucleophlicfunctional group. In some implementations, the portion of the surface ofthe coating terminated with at least one electrophilic functional groupand the portion of the surface of the coating terminated with at leastone nucleophilic functional group may be adjacent to one another. Thisconfiguration may be desirable for some implementations because itallows for the selective formation of adsorbing and non-adsorbingregions on the substrate. A method of forming such surfaces is describedin detail below.

In one non-limiting example of a method for chemically modifying thesurface of a substrate or base layer such as the structural layersdescribed above, a composition comprising at least one precursor isexposed to an energy source to form an energized precursor. Theenergized precursor is promoted into an excited state to produce ionicmaterials. The ionic materials are deposited on a base layer such thatthe ionic materials form a coating thereon. As described above, thecoating may comprise a chemically crosslinked material comprisingelements selected from the group consisting of (1) M, O, C, H, and N,wherein M is a metal selected from the group consisting of silicon,titanium, tantalum, germanium, boron, zirconium, aluminum, hafnium andyttrium; (2) M, O, H, and N, wherein M is defined above; (3) C; (4) O,C, H, and N; and (5) M or C, and one of O, H, or N. The chemicallycrosslinked material may be treated such that the material is terminatedwith at least one electrophilic or nucleophilic functional group. As anexample, a gas plasma treatment using reactive but non-polymerizinggases such as oxygen, nitrogen or ammonia may be used to modify thesurface free energy or charge potential of the gas plasma coating. Forexample, when oxygen is used for post-treatment, the resulting surfacehas oxygen containing functional groups such as —COOH and —OH and ishydrophilic. The treatment also imparts a negative charge to the surfacebecause oxygen containing functionalities are negatively charged. Forbiocompatibility, the surface charge may serve as an advantage to repelplatelets, cells and proteins which tend to have a net negative charge.As another example, when nitrogen or ammonia are utilized for thepost-treatment, the coating can be terminated using amine functionalgroups, which also results in a hydrophilic surface. Thus, the type ofpost-treatment can achieve the properties desired for a particularapplication. For example, nitrogen or ammonia gas plasma treatments oncertain conventional polymers have shown improved biocompatibility. C.P. Sharma, T. Chandy, and M. C. Sunny, Journal of BiomaterialsApplication, 1, (1987), 533; C. P. Shama, and P. R. Hari, Journal ofBiomaterials Application, 6, (1991), 72; C. P. Sharma, G. Jayashree, andP. P. Najeeb, Journal of Biomaterials Application, 2, 1987, 205, all ofwhich are respectively incorporated by reference herein in theirentireties.

The barrier coating may also be applied to the substrate or base layerto form an implantable electrode. As an example, an electricallyconducting intermediate layer may be present between the coating and thebase layer. The intermediate layer may comprise one or more electricallyconducting metals or metal alloys such as, without limitation, platinum,gold, and/or palladium, as well as one or more electrically conductingdoped and undoped oxides such as, without limitation, indium-doped tinoxide (ITO), tin oxide, titanium oxide, manganese oxide, zinc oxide, andlead oxide, as well as materials including, without limitation, gold,platinum, palladium, carbon, silicon, germanium, cadmium sulfide,titanium dioxide, and gallium arsenide. Combinations and alloys of theabove may also be employed. In one aspect, the intermediate layer istypically utilized to form an electrode whose active electrode openingis defined by an opening in the coating while the connection leads thatprovide electrical contacts to the working electrode are encapsulated bythe coating. In another aspect, the coating is capable of providing anon-adsorbing surface for various materials (e.g., large biomolecules),which otherwise may possibly be lost for electrochemical detection dueto adsorption to surfaces surrounding the electrode openings.

The patterning of the intermediate layer may be carried out by employinga number of techniques such as, for example, wet etching, lift off,shadow masking, screen printing, and the like. These procedures areillustrated in greater detail herein. The intermediate layer may beemployed in such a manner to form a number of various patterns incombination with the coating and the base layer. For example, thecoating may be selectively removed such that openings are formed thereinto allow the intermediate layer to be exposed. In another example, theintermediate layer and the coating present thereon are removed in amanner to expose the base layer underneath the intermediate layer andcoating layer. Alternatively, the intermediate layer and the coating maybe present such that the base layer is completely encapsulated.

As an example of depositing the coating, the coating may be depositedutilizing a PECVD process by employing the following parameters andprecursor gas. First, an argon and oxygen plasma treatment may beutilized to clean the substrate surface prior to the deposition of thepassivation layer. This step is intended to remove adsorbed organicimpurities from the surface to allow for good adhesion of the coating.The following conditions may be employed: gas mixture: 50 percent argonand 50 percent oxygen; processing pressure: 50 mTorr; bias voltage: −250V; processing time: 10 min. Next, a passivation layer may be depositedon the substrate employing the following conditions: active precursor:tetra methyl silane Si(CH₃)₄, 3 percent in argon; processing pressure:50 mTorr; bias voltage: −250 V. This may result in a coating thicknessof approximately 300 nm. Next, plasma surface activation may beperformed as the terminating step. It should be appreciated, however,that this step is optional, depending on the surface adsorptionproperties desired. Thus, this step is non-limiting. In an attempt tominimize or avoid non-specific adsorption of nucleic acids and proteins,an oxygen plasma treatment is performed to terminate the coating surfacewith functional groups having negative polarities. Nucleic acids beingpolyanions are believed to not adsorb to these negative functionalities,which may be highly advantageous in various implementations. Thefollowing processing conditions may be employed: processing gas: 100percent oxygen; processing pressure: 50 mTorr; bias voltage: −250 V;processing time: 1 min.

As examples of patterning an intermediate layer, various techniques maybe utilized. In the case of a wet etching technique, a photoresist maybe deposited and patterned as an etch mask on top of a blanket coatedintermediate layer. The intermediate layer ay be selectively etched bybringing exposed areas of intermediate layer in contact with a chemicaletchant. The etch mask may then be removed. In the case of a lift-offtechnique, a photoresist may be deposited and patterned on top of thesurface of the base layer. Material for the intermediate layer may bevacuum-depotied on top of base layer. The photoresist may then beremoved, thereby lifting off portions of the intermediate layer thatwere deposited on top of photoresist and leaving the patternedintermediate layer behind. In the case of a shadow masking technique,intermediate layer may be patterned during the deposition of theintermediate layer by bringing a foil containing defined openings indirect contact with the surface of the base layer. In such a way, thematerial for the intermediate layer is only deposited on the base layerat the locations of the foil openings. In the case of a screen printingtechnique, paste containing material for intermediate layer may bescreen printed through a screen or stencil resembling desired pattern ofthe intermediate layer on top of the base layer.

As examples of patterning a PECVD coating, various techniques may beutilized. In the case of a lift-off technique, a photoresist may bedeposited and patterned on top of the surface of the base layer. ThePECVD coating may be vacuum deposited on top of the base layer. Thephotoresist may then be removed, thereby lifting off portions of PECVDcoating that were deposited on top of photoresist and leaving patternedPECVD coating behind. In the case of shadow masking, the PECVD coatingmay be patterned during its deposition by bringing a foil containingdefined openings in direct contact with the surface of the base layer,the intermediate layer, or both, in such a way that the PECVD coating isonly deposited at the locations of the foil openings. In the case ofplasma etching, PECVD coating may be patterned by etching selectedregions of the coating after deposition. In this dry etching mode,selected regions of the coating may be protected from the etchingenvironment either by applying photoresist or covering these regionswith a shadow mask. The etching environment may comprise reactive gasplasma using gases such as, without limitation, oxygen, a fluorinecontaining gas such as carbon tetrafluoride or sulphur hexafluoride, ormixtures of oxygen and the fluorine containing gas. The PECVD coatingcan also be selectively removed by ion milling or sputtering using aninert gas plasma or ion beam source.

In addition to in vitro and in vivo applications, the packagedelectronic device may be configured for use as a sensor, a diagnostictool, or other type of instrument in more traditional operatingenvironments. For example, the device may be utilized in a detectionsystem such as, without limitation, an electrochemical detection system,a chemical detection system, an optical detection system, or amicrofluidic system. As an example, the microfluidic system may includeat least one biofouling surface.

Additional Embodiments

In addition to methods described above, the present disclosure providesthe following methods:

1. A method for fabricating a packaged electronic device, the methodcomprising: forming a plurality of electrical conductors on a firststructural layer; depositing an attachment layer on the electricalconductors and the first structural layer; placing a die including diecircuitry on the attachment layer to bond the die to the firststructural layer; forming a plurality of interconnects extending fromthe die circuitry, through the die, through the attachment layer, andinto contact with respective electrical conductors; depositing a secondstructural layer on the die and exposed portions of the electricalconductors, wherein the first structural layer and the second structurallayer encapsulate the die, the die circuitry and the electricalconductors; and forming a plurality of openings through at least one ofthe first structural layer and the second structural layer to exposerespective areas of the electrical conductors.

2. The method of embodiment 1, comprising forming through-holes in thedie prior to placing the die on the attachment layer, wherein placingthe die comprises aligning the through-holes with respective electricalconductors, and further comprising removing exposed portions of theattachment layer to extend the through-holes through the attachmentlayer to the respective electrical conductors, wherein forming theinterconnects comprises depositing interconnect material in thethrough-holes.

3. The method of embodiment 1, comprising forming through-holes throughthe die and the attachment layer, wherein forming the interconnectscomprises depositing interconnect material in the through-holes.

4. The method of embodiment 1, wherein the die has a thickness rangingfrom 10 μm to 50 μm.

5. The method of embodiment 1, wherein the attachment layer has athickness ranging from 0.5 μm to 5 μm.

6. The method of embodiment 1, wherein the first structural layer has athickness ranging from 2 μm to 100 μm.

7. The method of embodiment 1, wherein the second structural layer has athickness ranging from 2 μm to 100 μm.

8. The method of embodiment 1, wherein the attachment layer includes apolymer selected from the group consisting of polyimide, copolymers ofpolyimide, blends of polyimide, polyparaxylylene, liquid-crystalpolymers, and benzocyclobutene.

9. The method of embodiment 1, wherein the first structural layerincludes a polymer selected from the group consisting of polyimide,copolymers of polyimide, blends of polyimide, polyparaxylylene,liquid-crystal polymers, and benzocyclobutene.

10. The method of embodiment 1, wherein the second structural layerincludes a polymer selected from the group consisting of polyimide,copolymers of polyimide, blends of polyimide, polyparaxylylene,liquid-crystal polymers, and benzocyclobutene.

11. The method of embodiment 1, wherein the first structural layer, thesecond structural layer and the attachment layer each include a polymerselected from the group consisting of polyimide, copolymers ofpolyimide, blends of polyimide, polyparaxylylene, liquid-crystalpolymers, and benzocyclobutene.

12. The method of embodiment 1, comprising depositing a barrier film onat least one of the first structural layer and the second structurallayer.

13. The method of embodiment 12, wherein the barrier film compriseselements selected from the group consisting of (1) M, O, C, H, and N,wherein M is a metal selected from the group consisting of silicon,titanium, tantalum, germanium, boron, zirconium, aluminum, hafnium andyttrium; (2) M, O, H, and N; (3) C; (4) O, C, H, and N; and (5) M or C,and one of O, H, or N.

14. The method of embodiment 13, wherein the barrier film comprisesdiamond-like carbon.

15. The method embodiment 12, comprising terminating the barrier filmwith at least one of an electrophilic functional group or a nucleophilicfunctional group.

16. The method of embodiment 12, comprising modifying a surface of thebarrier film such that the barrier film is hydrophilic, hydrophobic,adsorptive of a desired biomaterial, or non-adsorptive of a desiredbiomaterial.

17. The method of embodiment 1, wherein the die is a first die, andfurther comprising placing a second die on the attachment layer or anadditional attachment layer in a planar arrangement with the first die,and forming a plurality of interconnects extending from die circuitry ofthe second die, through the second die, through the attachment layer oradditional attachment layer, and into contact with respective electricalconductors, wherein the second structural layer is deposited on thesecond die and both the first die and the second die are encapsulated bythe first structural layer and the second structural layer.

18. The method of embodiment 1, wherein the die is a first die and theattachment layer bonding the first die to the first structural layer isa first attachment layer, and further comprising depositing a secondattachment layer to the first die, placing a second die on the secondattachment layer to bond the second die to the first die, and formingone or more interconnects extending from die circuitry of the seconddie, through the second die, and in electrical contact with the diecircuitry of the first die, wherein the second structural layer isdeposited on the second die and both the first die and the second dieare encapsulated by the first structural layer and the second structurallayer.

19. The method of embodiment 1, wherein forming the plurality ofelectrical conductors comprises forming a plurality of layers ofelectrical conductors, and further comprising depositing one or moreintermediate flexible structural layers such that each intermediateflexible structural layer is interposed between two neighboring layersof electrical conductors.

20. The method of embodiment 1, wherein the plurality of openings isformed in the second structural layer and is on the same side of theelectrical conductors as the die.

21. The method of embodiment 1, wherein the plurality of openings isformed in the first structural layer and is on an opposite side of theelectrical conductors as the die.

22. The method of embodiment 1, wherein one or more of the openings areformed in the first structural layer and the other opening or openingsare formed in the second structural layer, such that one or moreopenings are on the same side of the electrical conductors as the dieand one or more openings are on an opposite side of the electricalconductors as the die.

One or more aspects, features, components, method steps and the likedisclosed herein may be applicable to those disclosed in U.S. patentapplication Ser. No. 12/333,448, filed Dec. 12, 2008, titled,“ELECTRONIC DEVICES INCLUDING FLEXIBLE ELECTRICAL CIRCUITS AND RELATEDMETHODS,” which is incorporated by reference herein in its entirety.Implementations utilizing or combining subject matter specificallydisclosed herein and in U.S. patent application Ser. No. 12/333,448 areencompassed by the present disclosure.

It will be understood that various aspects or details of the inventionmay be changed without departing from the scope of the invention.Furthermore, the foregoing description is for the purpose ofillustration only, and not for the purpose of limitation—the inventionbeing defined by the claims.

What is claimed is:
 1. A packaged electronic device, comprising: aflexible circuit structure comprising a first structural layer and aplurality of electrical conductors disposed on the first structurallayer, the plurality of electrical conductors comprising a plurality ofrespective first ends and a plurality of respective second ends; a diecomprising a first surface, an opposing second surface, and diecircuitry formed on the first surface, the die bonded to the flexiblecircuit structure by a flexible attachment layer interposed between thesecond surface and the first structural layer, the die furthercomprising a plurality of through-wafer interconnects in electricalcontact with the die circuitry and extending through the die, throughthe flexible attachment layer, and into electrical contact with therespective electrical conductors at the first ends; a flexible secondstructural layer disposed on the die and exposed portions of theelectrical conductors, wherein the die and the electrical conductors areencapsulated by the first structural layer and the second structurallayer; and wherein at least one of the first structural layer and thesecond structural layer comprises a plurality of openings definingrespective exposed areas on the electrical conductors at the secondends.
 2. The packaged electronic device of claim 1, wherein the dieincludes a material selected from the group consisting ofsemiconductors, compound semiconductors, metalloids, ceramics, glasses,polymers, and metals.
 3. The packaged electronic device of claim 1,wherein the die is sufficiently thin that the packaged electronic deviceis rollable into a cylinder having an outermost radius of 1 mm or less.4. The packaged electronic device of claim 1, wherein the die has athickness ranging from 10 μm to 50 μm.
 5. The packaged electronic deviceof claim 1, wherein the attachment layer has a thickness ranging from0.5 μm to 5 μm.
 6. The packaged electronic device of claim 1, whereinthe first structural layer has a thickness ranging from 2 μm to 100 μm.7. The packaged electronic device of claim 1, wherein the secondstructural layer has a thickness ranging from 2 μm to 100 μm.
 8. Thepackaged electronic device of claim 1, wherein the attachment layerincludes a polymer selected from the group consisting of polyimide,copolymers of polyimide, blends of polyimide, polyparaxylylene,liquid-crystal polymers, and benzocyclobutene.
 9. The packagedelectronic device of claim 1, wherein the first structural layerincludes a polymer selected from the group consisting of polyimide,copolymers of polyimide, blends of polyimide, polyparaxylylene,liquid-crystal polymers, and benzocyclobutene.
 10. The packagedelectronic device of claim 1, wherein the second structural layerincludes a polymer selected from the group consisting of polyimide,copolymers of polyimide, blends of polyimide, polyparaxylylene,liquid-crystal polymers, and benzocyclobutene.
 11. The packagedelectronic device of claim 1, wherein the first structural layer, thesecond structural layer and the attachment layer each include a polymerselected from the group consisting of polyimide, copolymers ofpolyimide, blends of polyimide, polyparaxylylene, liquid-crystalpolymers, and benzocyclobutene.
 12. The packaged electronic device ofclaim 1, further comprising a barrier film disposed on at least one ofthe first structural layer and the second structural layer.
 13. Thepackaged electronic device of claim 12, wherein the barrier filmcomprises elements selected from the group consisting of (1) M, O, C, H,and N, wherein M is a metal selected from the group consisting ofsilicon, titanium, tantalum, germanium, boron, zirconium, aluminum,hafnium and yttrium; (2) M, O, H, and N; (3) C; (4) O, C, H, and N; and(5) M or C, and one of O, H, or N.
 14. The packaged electronic device ofclaim 13, wherein the barrier film comprises diamond-like carbon. 15.The packaged electronic device of claim 12, wherein the barrier film isterminated with at least one of an electrophilic functional group or anucleophilic functional group.
 16. The packaged electronic device ofclaim 12, wherein the barrier film has a surface modified to behydrophilic, hydrophobic, adsorptive of a desired biomaterial, ornon-adsorptive of a desired biomaterial.
 17. The packaged electronicdevice of claim 1, wherein at least one of the first structural layerand the second structural layer is biocompatible.
 18. The packagedelectronic device of claim 1, wherein the flexible circuit structureincludes an elongated cable portion, and the openings that define theexposed areas on the electrical conductors are disposed in the cableportion.
 19. The packaged electronic device of claim 18, furtherincluding a remote device attached to the cable portion and electricallycommunicating with the electrical conductors through the openings. 20.The packaged electronic device of claim 19, wherein the remote deviceincludes an array of microelectrodes.
 21. The packaged electronic deviceof claim 1, comprising a second die bonded to the flexible circuitstructure by a second flexible attachment layer interposed between thesecond die and the first structural layer, the second die comprisingsecond die circuitry and a plurality of second through-waferinterconnects in electrical contact with the second die circuitry andextending through the second die, through the second flexible attachmentlayer, and into contact with the respective electrical conductors atrespective intermediate locations of the electrical conductors betweenthe first ends and the second ends, wherein the second die isencapsulated by the first structural layer and the second structurallayer.
 22. The packaged electronic device of claim 1, wherein the diebonded to the flexible circuit structure is a first die, and furthercomprising a second die bonded to the first die by a second flexibleattachment layer interposed between the second die and the firstsurface, the second die comprising second die circuitry and one or moresecond through-wafer interconnects in electrical contact with the seconddie circuitry and extending through the second die, through the secondflexible attachment layer, and into contact with the die circuitry ofthe first die, wherein the second die is encapsulated by the firststructural layer and the second structural layer.
 23. The packagedelectronic device of claim 1, wherein the plurality of electricalconductors is arranged as a plurality of layers of electricalconductors, and further comprising one or more intermediate flexiblestructural layers, each intermediate flexible structural layerinterposed between two neighboring layers of electrical conductors. 24.The packaged electronic device of claim 1, wherein the plurality ofopenings is formed in the second structural layer and is on the sameside of the electrical conductors as the die.
 25. The packagedelectronic device of claim 1, wherein the plurality of openings isformed in the first structural layer and is on an opposite side of theelectrical conductors as the die.
 26. The packaged electronic device ofclaim 1, wherein one or more of the openings are formed in the firststructural layer and the other opening or openings are formed in thesecond structural layer, such that one or more openings are on the sameside of the electrical conductors as the die and one or more openingsare on an opposite side of the electrical conductors as the die.